Image coding apparatus, method for coding image, program therefor, image decoding apparatus, method for decoding image, and program therefor

ABSTRACT

An image processing apparatus includes a division unit configured to divide an input image into a plurality of subblocks subjected to quantization control a subblock quantization parameter calculation unit configured to calculate a quantization parameter of each of the subblocks, a basic block quantization parameter calculation unit configured to set a basic block including at least two subblocks and to calculate a quantization parameter of the basic block, a difference value calculation unit configured to calculate a difference value between the quantization parameter of the basic block and the quantization parameter of each subblock included in the basic block, and a difference value coding unit configured to code the difference value.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/014,394 filed on Feb. 3, 2016, which is a continuation of Ser. No.14/003,776 filed on Sep. 6, 2013 as a National Stage applicationpursuant to 35 U.S.C. 371 (which issued as U.S. Pat. No. 9,277,221),which claims the benefit of PCT/JP2012/001319 filed Feb. 27, 2012, andJapanese Patent Application No. 2011-051267 filed Mar. 9, 2011. Theabove applications are hereby incorporated by reference herein in theirentirety.

TECHNICAL FIELD

The present invention relates to an image coding apparatus, a method forcoding an image, a program therefor, an image decoding apparatus, amethod for decoding an image, and a program therefor. More particularly,the present invention relates to a predictive coding method forquantization parameters in an image.

BACKGROUND ART

As a method for compressing and recording a moving image, theH.264/MPEG-4AVC (hereafter referred to as H.264) is known (ISO/IEC14496-10; 2004 Information technology—Coding of audio-visual objectsPart 10: Advanced Video Coding). The H.264 is widely used forone-segment terrestrial digital broadcasting.

The H.264 enables changing quantization parameters in macroblock units(16×16 pixels) by using the mb_qp_delta code. A formula 7-23 discussedin the above-mentioned document adds a difference value mb_qp_delta to aquantization parameter QPYPREV of a macroblock last decoded to changequantization parameters in macroblock units (16×16 pixels).

In recent years, an activity for internationally standardizing the HighEfficiency Video Coding (HEVC) has been started. (The HEVC is a stillhigher efficiency coding method which is a successor of the H.264.) Thisactivity, with the increase in screen size, considers division by largerblock sizes than conventional macroblocks (16×16 pixels). According toJCT-VC contribution JCTVC-A205.doc, a basic block having a larger sizeis referred to as Largest Coding Tree Block (LCTB). The considerationpremises a size of 64×64 pixels (JCT-VC contribution JCTVC-A205.doc<http://wftp3.itu.intlav-arch/jctvc-site/2010_04_A_Dresden/>). The LCTBis further divided into a plurality of subblocks. i.e., Coding TreeBlocks (CTBs) subjected to transform and quantization. As a divisionmethod, a region quadtree structure is used to divide a block into foursubblocks (two vertically and two horizontally).

FIG. 2A illustrates the region quadtree structure. A thick frame 10000indicates a basic block which is formed of 64×64 pixels to simplifydescriptions. Each of subblocks 10001 and 10010 is formed of 16×16pixels. Each of subblocks 10002 to 10009 is formed of 8×8 pixels.Subblocks are formed in this way and used for transform and other codingprocessing.

With the HEVC, it is considered that quantization parameter control isperformed on a basic block basis in a similar way to macroblocks of theH.264. However, from the viewpoint of image quality, it is actuallydesirable to perform quantization parameter control on a subblock basis.In this case, quantization in smaller units is expected to be performedthrough quantization parameter control on a subblock basis.

However, processing is performed based on the region quadtree structureeven if quantization in smaller units is possible. Therefore, it has notbeen possible to efficiently perform parallel processing on a subblockbasis, disabling improvement in coding and decoding processing speed.Specifically, referring to FIG. 2A, the subblock 10001 (16×16 pixels),the subblocks 10002 to 10009 (8×8 pixels), and the subblock 10010 (16×16pixels) are processed in this order. Since each of subblock quantizationparameters is calculated by using a difference value from a quantizationparameter of the preceding subblock as a predicted value, thesequantization parameters needs to be subjected to successive processing,thus disabling efficient parallel processing on a subblock basis.

Further, when quantization parameter optimization is attempted for eachsubblock, difference values will vary since processing for acquiring aquantization parameter difference value is performed based on the regionquadtree structure. For example, FIG. 2B illustrates a quantizationparameter value indicated at the center of each subblock. The example inFIG. 2B assumes a case where quantization parameter values graduallychange from the top left to the bottom right. This phenomenon is likelyto occur in ordinary natural images. Since the subblock 10001 has aquantization parameter of 12 and the subblock 10002 has a quantizationparameter of 14, the subblock 10002 has a difference value of +2 fromthe subblock 10001. Subsequent difference values are +4, −6, +6, −6,+−0, +2, +4, and +2. Acquiring difference values according to the regionquadtree structure in this way randomly fluctuates difference values,causing a problem that large codes are generated.

SUMMARY OF INVENTION

The present invention is directed to enabling coding and decoding foreach subblock to be performed in parallel to achieve not only high-speedprocessing but also high-efficiency quantization parameter coding anddecoding.

According to an aspect of the present invention, an image codingapparatus includes: division means configured to divide an input imageinto a plurality of subblocks subjected to quantization control:subblock quantization parameter calculation means configured tocalculate a quantization parameter of each of the subblocks; basic blockquantization parameter calculation means configured to set a basic blockincluding at least two subblocks and to calculate a quantizationparameter of the basic block; difference value calculation meansconfigured to calculate a difference value between the quantizationparameter of the basic block and the quantization parameter of eachsubblock included in the basic block; and difference value coding meansconfigured to code the difference value.

According to an exemplary embodiment of the present invention, it ispossible to independently code and decode each subblock quantizationparameter based on a basic block quantization parameter on a subblockbasis, facilitating parallel processing on a subblock basis. Further,restraining a prediction error enables high-efficiency quantizationparameter coding and decoding.

Further features and aspects of the present invention will becomeapparent from the following detailed description of exemplaryembodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate exemplary embodiments, features,and aspects of the invention and, together with the description, serveto explain the principles of the invention.

FIG. 1 is a block diagram illustrating a configuration of an imagecoding apparatus according to a first exemplary embodiment of thepresent invention.

FIG. 2A illustrates example block division.

FIG. 2B illustrates example block division.

FIG. 3 is a detailed block diagram illustrating a quantization parametercoding unit in the image coding apparatus according to the firstexemplary embodiment of the present invention.

FIG. 4 is a flowchart illustrating image coding processing by the imagecoding apparatus according to the first exemplary embodiment of thepresent invention.

FIG. 5A illustrates parallel processing at the time of coding.

FIG. 5B illustrates parallel processing at the time of coding.

FIG. 6 is a block diagram illustrating a configuration of an imagedecoding apparatus according to a second exemplary embodiment of thepresent invention.

FIG. 7 is a detailed block diagram illustrating a quantization parameterdecoding unit according to the second exemplary embodiment of thepresent invention.

FIG. 8 is a flowchart illustrating image decoding processing by theimage decoding apparatus according to the second exemplary embodiment ofthe present invention.

FIG. 9A illustrates parallel processing in decoding.

FIG. 9B illustrates parallel processing in decoding.

FIG. 10 is a block diagram illustrating a configuration of an imagecoding apparatus according to a third exemplary embodiment of thepresent invention.

FIG. 11 is a detailed block diagram illustrating a quantizationparameter coding unit in an image coding apparatus according to thethird exemplary embodiment of the present invention.

FIG. 12 is a flowchart illustrating image coding processing by the imagecoding apparatus according to the third exemplary embodiment of thepresent invention.

FIG. 13 is a block diagram illustrating a configuration of an imagedecoding apparatus according to a fourth exemplary embodiment of thepresent invention.

FIG. 14 is a detailed block diagram illustrating a quantizationparameter decoding unit in the image decoding apparatus according to thefourth exemplary embodiment of the present invention.

FIG. 15 is a flowchart illustrating image decoding processing by theimage decoding apparatus according to the fourth exemplary embodiment ofthe present invention.

FIG. 16 is a detailed block diagram illustrating a quantizationparameter coding unit in an image coding apparatus according to a fifthexemplary embodiment of the present invention.

FIG. 17 is a flowchart illustrating image coding processing by the imagecoding apparatus according to the fifth exemplary embodiment of thepresent invention.

FIG. 18 is a detailed block diagram illustrating a quantizationparameter decoding unit in an image decoding apparatus according to asixth exemplary embodiment of the present invention.

FIG. 19 is a flowchart illustrating image decoding processing by theimage decoding apparatus according to the sixth exemplary embodiment ofthe present invention.

FIG. 20 is a block diagram illustrating an example hardwareconfiguration of a computer applicable to the image coding apparatus andthe image decoding apparatus according to the exemplary embodiments ofthe present invention.

DESCRIPTION OF EMBODIMENTS

Various exemplary embodiments, features, and aspects of the inventionwill be described in detail below with reference to the drawings.

FIG. 1 is a block diagram illustrating an image coding apparatusaccording to a first exemplary embodiment of the present invention.Referring to FIG. 1, the image coding apparatus inputs image data from aterminal 1000.

A block division unit 1001 divides the input image into a plurality ofbasic blocks. i.e., clips a basic block from the input image a pluralityof number of times, and, if necessary, further divides each basic blockinto a plurality of subblocks. The image coding apparatus performsquantization control on a subblock basis. Although the input image isassumed to have 8-bit pixel values to simplify descriptions, the pixelvalue is not limited thereto. The size of a basic block is 64×64 pixels,and a minimum size of a subblock is 8×8 pixels. In this case, the basicblock includes four subblocks. Although block division will be describedbelow based on a method for dividing a block into four subblocks (twovertically and two horizontally), the shape and size of blocks are notlimited thereto. The basic block needs to include at least twosubblocks. Subblock division is not limited to any particular method.For example, the entire image may be divided into a plurality ofsubblocks after edge amount calculation and clustering. Specifically,small subblocks are set at a portion where there are many edges, andlarge subblocks are set at a flat portion. A quantization parameterdetermination unit 1002 determines a quantization parameter of eachbasic block and a quantization parameter of each subblock.

A block prediction unit 1003 performs prediction on a subblock basisformed by the block division unit 1001 to calculate a prediction errorfor each subblock. The block prediction unit 1003 appliesintra-prediction to intra-frames of a still image and moving image, andalso applies motion compensation prediction to a moving image. A blocktransform unit 1004 applies the orthogonal transform to a predictionerror for each subblock to calculate an orthogonal transformcoefficient. The orthogonal transform is not limited to any particularmethod, and may be based on the discrete cosine transform and Hadamardtransform. A block quantization unit 1005 quantizes the above-mentionedorthogonal transform coefficient based on each subblock quantizationparameter determined by the quantization parameter determination unit1002. This quantization enables obtaining a quantization coefficient. Ablock coding unit 1006 applies variable-length coding to a quantizationcoefficient for each subblock acquired in this way to generatequantization coefficient code data. Coding is not limited to anyparticular method, and may be based on the Huffman code or arithmeticcode. A block reproduced image generation unit 1007 reproduces aprediction error by performing an inverse operation of the blockquantization unit 1005 and the block transform unit 1004 to generate adecoded image of the basic block based on a result of the processing bythe block prediction unit 1003. The reproduced image data is stored andused for prediction by the block prediction unit 1003.

A quantization parameter coding unit 1008 encodes the basic blockquantization parameter and each subblock quantization parameterdetermined by the quantization parameter determination unit 1002 togenerate quantization parameter code data.

An integration and coding unit 1009 generates header information andencodes related to prediction, and integrates the quantization parametercode data generated by the quantization parameter coding unit 1008 andthe quantization coefficient code data generated by the block codingunit 1006. The integration and coding unit 1009 outputs the generatedbit stream to the outside via a terminal 1010.

Image coding processing by the image coding apparatus according to thepresent exemplary embodiment will be described below. Although, in thepresent exemplary embodiment, moving image data is input in frame units,still image data for one frame may be input.

The block division unit 1001 inputs image data for one frame from theterminal 1000, and divides the image data into a plurality of basicblocks each being formed of 64×64 pixels. If necessary, the blockdivision unit 1001 further divides each basic block into a plurality ofsubblocks each being formed of at least 8×8 pixels. The quantizationparameter determination unit 1002 and the block prediction unit 1003input information about the division into subblocks and divided imagedata.

The block prediction unit 1003 performs prediction referring to thereproduced image stored in the block reproduced image generation unit1007, generates a prediction error, and outputs the generated predictionerror to the block transform unit 1004 and the block reproduced imagegeneration unit 1007. The block transform unit 1004 applies theorthogonal transform to the input prediction error, calculates anorthogonal transform coefficient, and outputs the calculated orthogonaltransform coefficient to the block quantization unit 1005.

In view of the amount of input codes occurring in each subblock, thequantization parameter determination unit 1002 determines an optimumquantization parameter based on the balance between the image qualityand the amount of codes on a subblock basis. For example, a techniquediscussed in Japanese Patent Application Laid-Open No. 4-323961 can beused. The quantization parameter determination unit 1002 outputs each ofthe determined subblock quantization parameters to the blockquantization unit 1005, the block reproduced image generation unit 1007,and the quantization parameter coding unit 1008.

The block quantization unit 1005 quantizes the orthogonal transformcoefficient (input from the block transform unit 1004) based on eachquantization parameter determined by the quantization parameterdetermination unit 1002 to generate a quantization coefficient. Theblock quantization unit 1005 outputs the generated quantizationcoefficient to the block coding unit 1006 and the block reproduced imagegeneration unit 1007. The block reproduced image generation unit 1007inputs the quantization coefficient, and reproduces an orthogonaltransform coefficient based on each quantization parameter determined bythe quantization parameter determination unit 1002. The block reproducedimage generation unit 1007 applies inverse orthogonal transform to thereproduced orthogonal transform coefficient to reproduce a predictionerror, generates a reproduced image based on the reproduced predictionerror and the pixel value referred to at the time of prediction, andstores the reproduced image. The block coding unit 1006 encodes thequantization coefficient to generate quantization coefficient code data,and outputs the generated quantization coefficient code data to theintegration and coding unit 1009.

The quantization parameter coding unit 1008 encodes on a basic blockbasis the quantization parameters determined by the quantizationparameter determination unit 1002.

FIG. 3 is a detailed block diagram illustrating the quantizationparameter coding unit 1008. Referring to FIG. 3, the quantizationparameter coding unit 1008 inputs via a terminal 1 each subblockquantization parameter from the quantization parameter determinationunit 1002 in FIG. 1. A quantization parameter storage unit 2 once storesthe input subblock quantization parameters. A basic block quantizationparameter determination unit 3 determines a basic block quantizationparameter based on each subblock quantization parameter stored in thequantization parameter storage unit 2. A basic block quantizationparameter coding unit 4 encodes the basic block quantization parameterto generate a basic block quantization parameter code. The basic blockquantization parameter coding unit 4 outputs via a terminal 5 thegenerated basic block quantization parameter code to the integration andcoding unit 1009 in FIG. 1. A subblock quantization parameter differenceunit 6 acquires a difference between the basic block quantizationparameter and each subblock quantization parameter. A subblockquantization parameter coding unit 7 encodes the difference to generatea subblock quantization parameter difference value code. The subblockquantization parameter coding unit 7 outputs via a terminal 8 thegenerated subblock quantization parameter difference value code to theintegration and coding unit 1009 in FIG. 1.

With the above-mentioned configuration, the quantization parameterstorage unit 2 stores on a basic block basis the subblock quantizationparameters input from the terminal 1. When all of the subblockquantization parameters are stored in the quantization parameter storageunit 2, the basic block quantization parameter determination unit 3calculates the basic block quantization parameter. With the presentexemplary embodiment, the basic block quantization parameterdetermination unit 3 calculates an average of subblock quantizationparameters. Referring to FIG. 2B, the average is 14.6. When thequantization parameter coding is performed on an integer basis, thebasic block quantization parameter determination unit 3 rounds off theaverage 14.6 and, therefore, sets the basic block quantization parameterto 15. The basic block quantization parameter determination unit 3outputs the determined basic block quantization parameter to the basicblock quantization parameter coding unit 4 and the subblock quantizationparameter difference unit 6. The basic block quantization parametercoding unit 4 encodes the input basic block quantization parameterthrough Golomb coding to generate a basic block quantization parametercode, and outputs the generated basic block quantization parameter codeto the outside via the terminal 5.

The subblock quantization parameter difference unit 6 calculates adifference between each subblock quantization parameter and the basicblock quantization parameter. Referring to FIG. 2B, difference valuesare −3, −1, +3, −3, +3, −3, −3, −1, −1, and +5 in order of the regionquadtree structure. The subblock quantization parameter difference unit6 outputs these difference values to the subblock quantization parametercoding unit 7. The subblock quantization parameter coding unit 7 encodesthese difference values together with the existence or absence of achange. The quantization parameter of the first subblock 10001 differsfrom the basic block quantization parameter or 15. The subblockquantization parameter coding unit 7 encodes a one-bit value “1”indicating a change and a difference value “−3” through Golomb coding,and outputs the resultant code to the outside via the terminal 8 assubblock quantization parameter difference value coded data.Subsequently, the subblock quantization parameter coding unit 7 encodesthe subblock quantization parameter difference value of the secondsubblock 10002. Since this difference value differs from the basic blockquantization parameter, the subblock quantization parameter coding unit7 outputs a Golomb code composed of a one-bit value “1” indicating achange and a subblock quantization parameter difference value “−1” tothe outside via the terminal 8. Subsequently, in a similar way to theabove, the subblock quantization parameter coding unit 7 encodes aone-bit value “1” indicating a change and a subblock quantizationparameter difference value to generate subblock quantization parameterdifference value coded data.

Referring back to FIG. 1, the integration and coding unit 1009 generatean image sequence, a frame header, and other codes. For each basicblock, the integration and coding unit 1009 acquires information such asthe prediction mode from the block prediction unit 1003 and encodes theinformation. Then, the integration and coding unit 1009 inputs the basicblock quantization parameter code from the quantization parameter codingunit 1008. Subsequently, the integration and coding unit 1009 integratesthe subblock quantization parameter difference value coded data and thequantization coefficient code data for each subblock, and outputs as abit stream the integrated data to the outside via the terminal 1010.

FIG. 4 is a flowchart illustrating image coding processing by the imagecoding apparatus according to the first exemplary embodiment of thepresent invention. In step S001, the integration and coding unit 1009generates a sequence, a frame header, and other codes, and outputs thegenerated codes to the outside via the terminal 1010.

In step S002, the block division unit 1001 sequentially clips each basicblock from the input image starting with the top left corner thereof.

In step S003, the block division unit 1001 further divides each basicblock into a plurality of subblocks.

In step S004, the quantization parameter determination unit 1002determines subblock quantization parameters. In step S005, the imagecoding apparatus determines a basic block quantization parameter basedon the subblock quantization parameters determined in step S004. Tosimplify descriptions, the image coding apparatus according to thepresent exemplary embodiment calculates an average of quantizationparameters of subblocks in the basic block as a basic block quantizationparameter.

In step S006, the image coding apparatus encodes the basic blockquantization parameter (determined in step S005) through Golomb coding,and outputs the resultant code as a basic block quantization parametercode.

In step S007, the image coding apparatus encodes the subblockquantization parameter on a subblock basis. When using a quantizationparameter which is the same as the basic block quantization parameter inorder of the region quadtree structure, the image coding apparatusoutputs a one-bit code “0”. When using a different quantizationparameter, the image coding apparatus outputs a one-bit code “1” and adifference between each subblock quantization parameter and the basicblock quantization parameter.

In step S008, the image coding apparatus performs prediction for thesubblock image data to obtain a prediction error, applies the orthogonaltransform and quantization to the prediction error, encodes the obtainedquantization coefficient, and outputs the quantization coefficient codedata.

In step S009, the image coding apparatus applies inverse quantizationand inverse transform to the obtained quantization coefficient tocalculate a prediction error. The image coding apparatus generates areproduced image of the relevant subblock based on the prediction errorand a predicted value obtained from the reproduced image.

In step S010, the image coding apparatus determines whether codingprocessing is completed for all the subblocks in the basic block. Whencoding processing is completed for all the subblocks (YES in step S010),the processing proceeds to step S011. Otherwise, when coding processingis not completed for all the subblocks (NO in step S010), the processingreturns to step S007 to process the following subblock.

In step S011, the image coding apparatus determines whether codingprocessing is completed for all the basic blocks. When coding processingis completed for all the basic blocks (YES in step S011), the processingends. Otherwise, when coding processing is not completed for all thebasic blocks (NO in step S011), the processing returns to step S002 toprocess the following basic block.

Particularly in steps S005 to S009, the above-mentioned configurationand operations enable coding each subblock quantization parameterdifference value by using the basic block quantization parameter, thusrestraining the amount of generated codes.

Although, in the present exemplary embodiment, an average of subblockquantization parameters is used as it is as a basic block quantizationparameter, the basic block quantization parameter is not limitedthereto, and may be an actual subblock quantization parameter valueclosest to the average. For example, although the average is 14.6 in theexample in FIG. 2B, the actual subblock quantization parameter valueclosest to the average, i.e., 14 may be used instead of a value obtainedby rounding off the average. Acquiring the subblock quantizationparameter in this way enables setting the code indicating a change to“0”, reducing the number of subblock quantization parameter differencevalues to be transmitted.

The above-mentioned configuration further enables efficiently performingprediction, quantization, transform, and coding in parallel, achievinghigh speed processing.

FIGS. 5A and 5B illustrate example parallel processing for applyingquantization, transform, and coding processing to the subblocks 10001 to10005 in the basic block 10000 illustrated in FIG. 2A. In this case,three processors are assumed to be used for coding processing tosimplify descriptions. The processors A to C calculate each subblockquantization parameter (QP), calculate and code each subblockquantization parameter difference value (.delta.QP), apply orthogonaltransform and quantization to the prediction error, and code thequantization coefficient. In this case, these codes are integrated byanother processor.

FIG. 5A illustrates example conventional parallel processing. First ofall, the image coding apparatus assigns the processing of the subblock10001 to the processor A, the processing of the subblock 10002 to theprocessor B, and the processing of the subblock 10003 to the processorC. Processing time for QP calculation depends on the block size andimage complexity. There is a tendency that quantization parametercalculation for the subblock 10001 having a larger block size takes alonger time than quantization parameter calculation for the subblocks10002 and 10003.

Following the quantization parameter calculation, the image codingapparatus calculates quantization parameter difference values. Thesubblock quantization parameter calculation for the subblock 10001 needsto be completed to start the subblock quantization parameter differencevalue calculation for the subblock 10002. This means that the processorB waits until the processor A completes the subblock quantizationparameter calculation for the subblock 10001. If it takes a longer timeto calculate the quantization parameter of the subblock 10002 than tocalculate that of the subblock 10003, the subblock quantizationparameter calculation for the subblock 10002 needs to be completed tostart the subblock quantization parameter difference value calculationfor the subblock 10003. The processor C waits until the processor Bcompletes the subblock quantization parameter calculation for thesubblock 10002.

FIG. 5B illustrates example parallel processing according to the presentexemplary embodiment. Similar to the conventional case, the image codingapparatus assigns the processing of the subblock 10001 to the processorA, the processing of the subblock 10002 to the processor B, and theprocessing of the subblock 10003 to the processor C. Following thesubblock quantization parameter calculation, the image coding apparatuscalculates subblock quantization parameter difference values. Since thebasic block quantization parameter calculation is completed, thesubblock quantization parameter difference value calculation for thesubblock 10002 can be started immediately after calculating the subblockquantization parameter. Thus, the present invention achieves efficientparallel processing. In particular, when subblocks having a plurality ofsizes exist, the present invention provides a profound effect ofreducing processing interval.

Although, in the present exemplary embodiment, the basic blockquantization parameter value itself is coded, prediction may beperformed by using a basic block quantization parameter processedbefore.

Although, in the present exemplary embodiment, a basic block is formedof 64×64 pixels, and a subblock is formed of up to 8×8 pixels, the pixelconfiguration is not limited thereto. For example, the block size of abasic block can be changed to 128×128 pixels. The shape of basic blockand subblock is not limited to a square, and may be a rectangle such as8×4 pixels. The essence of the present invention remains unchanged.

Although, in the present exemplary embodiment, an average of subblockquantization parameters is considered as a basic block quantizationparameter, the basic block quantization parameter is not limitedthereto. It is of course possible, for example, that the basic blockquantization parameter may be a median of subblock quantizationparameters, or a most frequent subblock quantization parameter value. Itis of course possible to prepare a plurality of calculation methods inthis way, and select a most efficient basic block quantizationparameter.

Although a one-bit code indicating a change is provided in the subblockquantization parameter difference value coded data, the processing isnot limited thereto. It is of course possible to encode the subblockquantization parameter difference value even when there is no change.

Although, in the present exemplary embodiment, Golomb coding is used toencode the basic block quantization parameter, the subblock quantizationparameter difference value, and the quantization coefficient, theprocessing is not limited thereto. It is of course possible to use, forexample, Huffman coding and other arithmetic coding methods, and outputthe above-mentioned values as they are without coding.

Although the present exemplary embodiment has specifically beendescribed based on frames using intra-prediction, it is apparent thatthe present exemplary embodiment is also applicable to frames that canuse inter-prediction involving motion compensation in prediction.

A second exemplary embodiment of the present invention will be describedbelow based on an image decoding method for decoding code data coded byusing the coding method according to the first exemplary embodiment ofthe present invention. FIG. 6 is a block diagram illustrating aconfiguration of an image decoding apparatus according to the secondexemplary embodiment of the present invention.

The image decoding apparatus inputs a coded bit stream from a terminal1100. The decoding and separation unit 1101 decodes the headerinformation of the bit stream, separates required codes from the bitstream, and outputs the separated codes to the subsequent stage. Thedecoding and separation unit 1101 performs an inverse operation of theintegration and coding unit 1009 in FIG. 1. A quantization parameterdecoding unit 1102 decodes quantization parameter coded data. A blockdecoding unit 1103 decodes each subblock quantization coefficient codeto reproduce a quantization coefficient. A block inverse quantizationunit 1104 applies inverse quantization to the quantization coefficientbased on the subblock quantization parameter reproduced by thequantization parameter decoding unit 1102 to reproduce an orthogonaltransform coefficient. A block inverse transform unit 1105 performsinverse orthogonal transform of the block transform unit 1004 in FIG. 1to reproduce a prediction error. A block reproduction unit 1106reproduces subblock image data based on the prediction error and thedecoded image data. A block combination unit 1107 arranges thereproduced subblock image data at respective positions to reproducebasic block image data.

Image decoding processing by the image decoding apparatus according tothe present exemplary embodiment will be described below. Although, inthe second exemplary embodiment, a moving image bit stream generated bythe image coding apparatus according to the first exemplary embodimentis input in frame units, a still image bit stream for one frame may beinput.

Referring to FIG. 6, the decoding and separation unit 1101 inputs thestream data for one frame from the terminal 1100, and decodes the headerinformation required to reproduce an image. Subsequently, the decodingand separation unit 1101 outputs the basic block quantization parametercode to the quantization parameter decoding unit 1102. Subsequently, thedecoding and separation unit 1101 also outputs the subblock quantizationparameter difference value code to the quantization parameter decodingunit 1102.

FIG. 7 is a detailed block diagram illustrating the quantizationparameter decoding unit 1102. The quantization parameter decoding unit1102 inputs via a terminal 101 the basic block quantization parametercode from the decoding and separation unit 1101 in FIG. 6. Thequantization parameter decoding unit 1102 also inputs via a terminal 102the subblock quantization parameter difference coded data from thedecoding and separation unit 1101 in FIG. 6. A basic block quantizationparameter decoding unit 103 inputs the basic block quantizationparameter code, and decodes the basic block quantization parameter codeto reproduce a basic block quantization parameter. A subblockquantization parameter decoding unit 104 decodes the subblockquantization parameter difference value coded data to reproduce eachsubblock quantization parameter difference value. A subblockquantization parameter adding unit 105 adds the reproduced basic blockquantization parameter and each subblock quantization parameterdifference value to reproduce each subblock quantization parameter. Thesubblock quantization parameter adding unit 105 outputs via a terminal106 each reproduced subblock quantization parameter to the block inversequantization unit 1104 in FIG. 6.

The basic block quantization parameter decoding unit 103 inputs thebasic block quantization parameter code from the terminal 101, decodesthe basic block quantization parameter code by using the Golomb code toreproduce a basic block quantization parameter, and stores the resultantcode.

The subblock quantization parameter decoding unit 104 inputs thesubblock quantization parameter difference value coded data from theterminal 102, and decodes the subblock quantization parameter differencevalue coded data by using the Golomb code to reproduce a subblockquantization parameter difference value. Specifically, the subblockquantization parameter decoding unit 104 decodes a one-bit codeindicating the presence or existence of a change with respect to thebasic block quantization parameter. When there is no change, thesubblock quantization parameter decoding unit 104 outputs zero as thesubblock quantization parameter difference value to the subblockquantization parameter adding unit 105. When there is a change, thesubblock quantization parameter decoding unit 104 subsequently decodesthe subblock quantization parameter difference value, and outputs theresultant value to the subblock quantization parameter adding unit 105.The subblock quantization parameter adding unit 105 adds the subblockquantization parameter difference value to the reproduced basic blockquantization parameter to reproduce a subblock quantization parameter,and outputs the reproduced subblock quantization parameter to theoutside via the terminal 106.

Referring back to FIG. 6, the block decoding unit 1103 inputs thesubblock quantization coefficient code data separated from the bitstream by the decoding and separation unit 1101, decodes the inputsubblock quantization coefficient code data by using the Golomb code toreproduce each subblock quantization coefficient, and outputs thereproduced subblock quantization coefficient to the block inversequantization unit 1104. The block inverse quantization unit 1104 appliesinverse quantization to the input subblock quantization coefficient andsubblock quantization parameter to reproduce an orthogonal transformcoefficient, and outputs the reproduced orthogonal transform coefficientto the block inverse transform unit 1105. The block inverse transformunit 1105 applies inverse transform to the reproduced orthogonaltransform coefficient to reproduce a prediction error, and outputs there-produced prediction error to the block reproduction unit 1106. Theblock reproduction unit 1106 inputs the reproduced prediction error,performs prediction based on the sur-rounding decoded pixel data orpreceding frame pixel data to reproduce subblock image data, and outputsthe reproduced subblock image data to the block combination unit 1107.The block combination unit 1107 arranges the reproduced subblock imagedata at respective positions to reproduce basic block image data, andoutputs the reproduced basic block image data to the outside via theterminal 1108. The block combination unit 1107 also outputs thereproduced basic block image data to the block reproduction unit 1106for predicted value calculation.

FIG. 8 is a flowchart illustrating image decoding processing by theimage decoding apparatus according to the second exemplary embodiment ofthe present invention. In step S101, the decoding and separation unit1101 decodes the header information.

In step S102, the basic block quantization parameter decoding unit 103decodes the basic block quantization parameter code to reproduce a basicblock quantization parameter.

In step S103, the subblock quantization parameter decoding unit 104decodes the subblock quantization parameter difference value coded datato reproduce a subblock quantization parameter difference value. Thesubblock quantization parameter adding unit 105 adds the basic blockquantization parameter to the subblock quantization parameter differencevalue to reproduce a subblock quantization parameter.

In step S104, the image decoding apparatus decodes the subblockquantization coefficient code data to reproduce a quantizationcoefficient, and applies inverse quantization and inverse orthogonaltransform to the decoded subblock quantization co-efficient code data toreproduce a prediction error. The image decoding apparatus furtherperforms prediction based on the surrounding decoded pixel data orpreceding frame pixel data to reproduce a subblock decoded image.

In step S105, the image decoding apparatus arranges the subblock decodedimage to the basic block decoded image. In step S106, the image decodingapparatus determines whether decoding processing is completed for allthe subblocks in the relevant basic block. When decoding processing iscompleted for all the subblocks (YES in step S106), the processingproceeds to step S107. When decoding processing is not completed for allthe subblocks (NO in step S106), the processing returns to step S103 toprocess the following subblock.

In step S107, the image decoding apparatus arranges the basic blockdecoded image to the frame decoded image. In step S108, the imagedecoding apparatus determines whether decoding processing is completedfor all the basic blocks. When decoding processing is completed for allthe basic blocks (YES in step S108), the image decoding apparatus stopsall operations to terminate processing. When decoding processing is notcompleted for all the basic blocks (NO in step S108), the processingreturns to step S102 for the following basic block.

The above-mentioned configuration and operations enable decoding a bitstream with reduced amount of codes, generated in the first exemplaryembodiment, to obtain the reproduced image.

If code identification is possible for each subblock by using adelimiter symbol, it is possible to effectively perform differentoperations in parallel, i.e., to reproduce subblock quantizationparameters, apply inverse quantization and inverse transform toreproduced subblocks, and reproduce image data, thus achievinghigh-speed decoding.

FIGS. 9A and 9B illustrate example parallel processing for applyingdecoding, inverse quantization, and inverse transform processing to thesubblocks 10001 to 10006 in the basic block 10000 illustrated in FIG. 2Ato reproduce prediction errors. Similar to FIGS. 5A and 5B according tothe first exemplary embodiment of the present invention, threeprocessors are assumed to be used to simplify descriptions. In thisexample, the three processors decode each subblock quantizationparameter difference value (.delta.QP) to reproduce a quantizationparameter (QP), decode the quantization coefficient, and applies inversequantization and inverse orthogonal transform to the quantizationcoefficient. In this case, another processor separates these codes.

FIG. 9A illustrates example conventional parallel processing. First ofall, the image decoding apparatus assigns the processing of the subblock10001 to the processor A, the processing of the subblock 10002 to theprocessor B, and the processing of the subblock 10003 to the processorC. Since the processor A, as a first processor, decodes the subblockquantization parameter itself. The processors B and C decode eachsubblock quantization parameter difference value, and then reproduce asubblock quantization parameter. The above-mentioned processing isachieved by adding the subblock quantization parameter of subblocksbefore becoming a subblock quantization parameter predicted value, andthe subblock quantization parameter difference value.

The decoding of the quantization parameter of the subblock 10001 needsto be completed to start the subblock quantization parameterreproduction for the subblock 10002. This means that the processor Bwaits until the processor A completes the quantization parameterreproduction for the subblock 10001.

This also applies to the quantization parameter reproduction for thesubblock 10002. The processor C waits until the processor B completesthe quantization parameter reproduction for the subblock 10002.Subsequently, each of processors that completed processing processessubblocks in order of the region quadtree structure, i.e., in order ofthe subblock 10004, the subblock 10005, and the subblock 10006. Thequantization parameter reproduction for the subblock 10005 needs to becompleted to start the subblock quantization parameter reproduction forthe subblock 10006. This means that the processor C waits until theprocessor A completes the quantization parameter reproduction for thesubblock 10005.

FIG. 9B illustrates example parallel processing according to the presentexemplary embodiment. First, the processor A decodes and stores thebasic block quantization parameter. Subsequently, similar to theconventional case, the image decoding apparatus assigns the processingof the subblock 10001 to the processor A, the processing of the subblock10002 to the processor B, and the processing of the subblock 10003 tothe processor C. After decoding the subblock quantization parameterdifference value, the image decoding apparatus reproduces a subblockquantization parameter. Since the basic block quantization parameter hasbeen reproduced, the quantization parameter reproduction for thesubblock 10002 can be started immediately after decoding the subblockquantization parameter difference value. The present invention achievesefficient parallel processing. In particular, when subblocks having aplurality of sizes exist, the present invention provides a profoundeffect on reducing processing interval.

Suppose a case where only a subblock 10008 in FIG. 2A is clipped byusing an editing application for clipping a part from image data. Withthe conventional case, the subblocks 10001 to 10007 need to be decoded.According to the present invention, decoding only the subblocks 10001and 10006 enables necessary decoding processing includingintra-prediction. Thus, the processing speed can be improved by skippingthe decoding processing.

Similar to the first exemplary embodiment of the present invention,block size, processing unit size, processing units referred to and pixelarrangements, and codes are not limited thereto.

Although, in the second exemplary embodiment, the Golomb code is used todecode the basic block quantization parameter, the subblock quantizationparameter difference value, and the quantization coefficient, theprocessing is not limited thereto. It is of course possible to use, forexample, Huffman coding and other arithmetic coding methods, and outputthe above-mentioned values as they are without coding.

Although the second exemplary embodiment has specifically been describedbased on frames using intra-prediction, it is apparent that the presentexemplary embodiment is also applicable to frames that can useinter-prediction involving motion compensation in prediction.

FIG. 10 is a block diagram illustrating an image coding apparatusaccording to a third exemplary embodiment of the present invention. Inthe third exemplary embodiment, a quantization parameter of the firstsubblock (hereinafter referred to as first subblock quantizationparameter) is considered as a basic block quantization parameter, andthe basic block quantization parameter is not encoded individually.Unlike the first exemplary embodiment of the present invention, thethird exemplary embodiment does not use a code indicating the existenceor absence of a change. However, similar to the first exemplaryembodiment of the present invention, coding may be performed by using acode indicating the existence or absence of a change. Referring to FIG.10, elements having the same function as those in the first exemplaryembodiment (FIG. 1) are assigned the same reference numerals andduplicated descriptions will be omitted.

A quantization parameter coding unit 1208 encodes a subblockquantization parameter to generate quantization parameter code data. Anintegration and coding unit 1209 generates header information and a coderelated to prediction, and integrates the quantization parameter codedata generated by the quantization parameter coding unit 1208 and thequantization coefficient code data generated by the block coding unit1006.

FIG. 11 is a detailed block diagram illustrating the quantizationparameter coding unit 1208. Referring to FIG. 11, elements having thesame function as those in the first exemplary embodiment (FIG. 3) areassigned the same reference numerals and duplicated descriptions will beomitted.

A selector 200 selects a destination depending on the subblock positionfor the input subblock quantization parameter. A basic blockquantization parameter storage unit 203 stores the first subblockquantization parameter as a basic block quantization parameter in orderof the region quadtree structure of the basic block. A subblockquantization parameter difference unit 206 calculates a difference valuebetween each of subsequent subblock quantization parameters and thebasic block quantization parameter. A subblock quantization parametercoding unit 207 encodes the first subblock quantization parameter andeach subblock quantization parameter difference value.

Similar to the first exemplary embodiment, the quantization parametercoding unit 1208 having the above-mentioned configuration inputssubblock quantization parameters from the terminal 1 in order of theregion quadtree structure. The selector 200 outputs the first subblockquantization parameter to the basic block quantization parameter storageunit 203 in order of the region quadtree structure. The selector 200outputs subsequent subblock quantization parameters to the subblockquantization parameter difference unit 206.

The basic block quantization parameter storage unit 203 stores the firstsubblock quantization parameter as a basic block quantization parameter.Then, the subblock quantization parameter difference unit 206 alsoinputs the first subblock quantization parameter. Since the relevantsubblock quantization parameter is the first subblock quantizationparameter in the basic block, the subblock quantization parameterdifference unit 206 does not calculate a difference and outputs therelevant subblock quantization parameter as it is to the subblockquantization parameter coding unit 207 on the subsequent stage. Thesubblock quantization parameter coding unit 207 encodes the inputsubblock quantization parameter through Golomb coding, and outputs theresultant code to the outside via the terminal 8 as subblockquantization parameter coded data.

Subsequently, the subblock quantization parameter difference unit 206inputs from the terminal 1 via the selector 200 subblock quantizationparameters in order of the region quadtree structure. The subblockquantization parameter difference unit 206 calculates a difference valuebetween each input subblock quantization parameter and the basic blockquantization parameter stored in the basic block quantization parameterstorage unit 203. The subblock quantization parameter coding unit 207encodes the subblock quantization parameter difference value throughGolomb coding to generate subblock quantization parameter differencevalue coded data, and outputs the generated subblock quantizationparameter difference value coded data to the outside via the terminal 8as subblock quantization parameter coded data. Subsequently, thesubblock quantization parameter coding unit 207 obtains and encodes asubblock quantization parameter difference value of each subblock in thebasic block.

FIG. 12 is a flowchart illustrating image coding processing by the imagecoding apparatus according to the third exemplary embodiment of thepresent invention. Referring to FIG. 12, elements having the samefunction as those in the first exemplary embodiment (FIG. 4) areassigned the same reference numerals and duplicated descriptions will beomitted.

In steps S001 to S004, similar to the first exemplary embodiment of thepresent invention, the image coding apparatus clips a basic block,divides the basic block into a plurality of subblocks, and determinessubblock quantization parameters.

In step S205, the image coding apparatus stores the first subblockquantization parameter as a basic block quantization parameter.

In step S206, the image coding apparatus determines whether the inputsubblock is the first subblock in the basic block. When the inputsubblock is the first subblock, the processing proceeds to step S208(YES in step S206). Otherwise, when the input subblock is not the firstsubblock (NO in step S206), the processing proceeds to step S207. Instep S207, the image coding apparatus calculates a difference betweenthe basic block quantization parameter stored in step S205 and the inputsubblock quantization parameter.

In step S208, the image coding apparatus encodes the input subblockquantization parameter or the subblock quantization parameter differencevalue through Golomb coding, and outputs the resultant code as subblockquantization parameter coded data.

In steps S008 and S009, the image coding apparatus performs similarprocessing to the image coding apparatus according to the firstexemplary embodiment of the present invention. In step S210, the imagecoding apparatus determines whether coding processing is completed forall the subblocks in the basic block. When coding processing is notcompleted for all the subblocks (NO in step S210), the processingproceeds to step S206 to process the following subblock. When codingprocessing is completed for all the subblocks (YES in step S210), theprocessing proceeds to step S011. Subsequently, the image codingapparatus performs coding processing for the entire image similar to theimage coding apparatus according to the first exemplary embodiment ofthe present invention. With the above-mentioned configuration andoperations, considering the first subblock quantization parameter as abasic block quantization parameter eliminates the need of transferringthe basic block quantization parameter, resulting in improved codingefficiency.

The above-mentioned configuration and operations further enableeffective parallel processing similar to the first exemplary embodimentof the present invention. Specifically, referring to FIG. 5A, at thefirst stage of parallel processing, the processors B and C need to waituntil the processor A completes the first subblock quantizationparameter calculation. Subsequently, however, the processors B and C cancalculate the quantization parameter difference value of the subblock10005 without waiting until the processor A completes the processing ofthe subblock 10004.

It is of course possible to provide a code for switching between themethod for coding the basic block quantization parameter in the firstexemplary embodiment and the method for considering the first subblockquantization parameter as a basic block quantization parameter in thepresent exemplary embodiment, and select whichever has higher codingefficiency.

Although the same coding method is applied to the first subblockquantization parameter (basic block quantization parameter) andsubsequent subblock quantization parameter difference values, theprocessing is not limited thereto. It is of course possible to applydifferent coding methods to the first subblock quantization parameterand subsequent subblock quantization parameter difference values.

Although, in the third exemplary embodiment, the basic blockquantization parameter, the subblock quantization parameter differencevalue, and the quantization coefficient are encoded through Golombcoding, the processing is not limited thereto. It is of course possibleto use, for example, Huffman coding and other arithmetic coding methods.

Although the third exemplary embodiment has specifically been describedbased on frames using intra-prediction, it is apparent that the presentexemplary embodiment is also applicable to frames that can useinter-prediction involving motion compensation in prediction.

A fourth exemplary embodiment of the present invention will be describedbelow based on an image decoding method for decoding code data coded byusing the coding method according to the third exemplary embodiment ofthe present invention. FIG. 13 is a block diagram illustrating an imagedecoding apparatus for decoding code data coded by using the codingmethod according to the third exemplary embodiment of the presentinvention. Referring to FIG. 13, elements having the same function asthose in the second exemplary embodiment (FIG. 6) are assigned the samereference numerals and duplicated descriptions will be omitted.

Referring to FIG. 13, a decoding and separation unit 1301 decodes theheader information of a bit stream, separates required codes from thebit stream, and outputs the separated codes to the subsequent stage. Aquantization parameter decoding unit 1302 reproduces a subblockquantization parameter. The decoding and separation unit 1301 and thequantization parameter decoding unit 1302 differs in quantizationparameter code data from the decoding and separation unit 1101 and thequantization parameter decoding unit 1102 (FIG. 6), respectively,according to the second exemplary embodiment.

Image decoding processing by the image decoding apparatus according tothe present exemplary embodiment will be described below. Although, inthe present exemplary embodiment, a moving image bit stream generated bythe image coding apparatus according to the third exemplary embodimentis input in frame units, a still image bit stream for one frame may beinput.

Similar to the second exemplary embodiment, the decoding and separationunit 1301 inputs stream data for one frame from the terminal 1100, anddecodes the header information required to reproduce an image.Subsequently, the quantization parameter decoding unit 1302 inputs thesubblock quantization parameter coded data in order of the regionquadtree structure.

FIG. 14 is a detailed block diagram illustrating the quantizationparameter decoding unit 1302. Referring to FIG. 14, elements having thesame function as those in the second exemplary embodiment (FIG. 7) areassigned the same reference numerals and duplicated descriptions will beomitted.

A subblock quantization parameter decoding unit 304 decodes the subblockquantization parameter and subblock quantization parameter differencevalue coded data to reproduce each subblock quantization parameterdifference value. A selector 300 selects a destination depending on thesubblock position for the input subblock quantization parameter. A basicquantization parameter storage unit 310 stores as a basic blockquantization parameter the subblock quantization parameter decodedfirst. A subblock quantization parameter adding unit 305 adds the basicblock quantization parameter and each subblock quantization parameterdifference value to reproduce each subblock quantization parameter.

With the above-mentioned configuration, the selector 300 selects thebasic block quantization parameter storage unit 310 as a destinationwhen decoding of the basic block is started. The subblock quantizationparameter decoding unit 304 inputs the subblock quantization parametercoded data of the first subblock in the basic block from the terminal102, and decodes the subblock quantization parameter coded data by usingthe Golomb code to reproduce a subblock quantization parameter. Thebasic block quantization parameter storage unit 310 inputs the firstsubblock quantization parameter via the selector 300, and stores thesubblock quantization parameter during processing of the relevant basicblock. Then, the subblock quantization parameter adding unit 305 alsoinputs the first subblock quantization parameter. Since the differencevalue does not exist for the first subblock, the subblock quantizationparameter adding unit 305 outputs the reproduced subblock quantizationparameter as it is to the outside via the terminal 106. When the basicblock quantization parameter storage unit 310 stores the first subblockquantization parameter, the selector 300 selects the subblockquantization parameter adding unit 305 as a destination.

Subsequently, the subblock quantization parameter decoding unit 304inputs the second and subsequent subblock quantization parameterdifference value coded data. The subblock quantization parameterdecoding unit 304 decodes the input subblock quantization parameterdifference value coded data by using the Golomb code to reproduce asubblock quantization parameter difference value. The subblockquantization parameter adding unit 305 adds the subblock quantizationparameter difference value (input via the selector 300) to the basicblock quantization parameter stored in the basic block quantizationparameter storage unit 310. The subblock quantization parameter addingunit 305 reproduces a subblock quantization parameter in this way, andoutputs the reproduced subblock quantization parameter to the outsidevia the terminal 106. Subsequently, the quantization parameter decodingunit 1302 decodes the subblock quantization parameter of each subblockin the basic block, calculates the subblock quantization parameterdifference value, and adds the calculated subblock quantizationparameter difference value to the basic block quantization parameter toreproduce a subblock quantization parameter.

FIG. 15 is a flowchart illustrating image decoding processing accordingto the fourth exemplary embodiment of the present invention. Referringto FIG. 15, elements having the same function as those in the secondexemplary embodiment (FIG. 8) are assigned the same reference numeralsand duplicated descriptions will be omitted.

In step S101, the image decoding apparatus decodes the headerinformation similar to the image decoding apparatus according to thesecond exemplary embodiment of the present invention. In step S310, theimage decoding apparatus determines whether the subblock subjected todecoding is the first subblock in the basic block. When the subblocksubjected to decoding is the first subblock (YES in step S310), theprocessing proceeds to step S311. Otherwise, when the subblock subjectedto decoding is not the first subblock (NO in step S310), the processingproceeds to step S303.

In step S311, the image decoding apparatus decodes the code related tothe input subblock quantization parameter, i.e., the subblockquantization parameter coded data by using the Golomb code, and storesthe resultant code as a basic block quantization parameter. Then, theprocessing proceeds to step S104 to generate a decoded image of thefirst subblock.

In step S303, the image decoding apparatus decodes the code related tothe input subblock quantization parameter, i.e., the subblockquantization parameter difference value coded data by using the Golombcode to reproduce a subblock quantization parameter difference value.The image decoding apparatus adds the reproduced subblock quantizationparameter difference value to the basic block quantization parameterstored in step S311, and uses a result of addition as a subblockquantization parameter. The processing proceeds to step S104 to generatedecoded images of the second and subsequent subblocks.

Subsequently, similar to the second exemplary embodiment of the presentinvention, the image decoding apparatus generates a subblock decodedimage and reproduces a frame image.

The above-mentioned configuration and operations enable decoding codeddata with reduced amount of codes generated in the third exemplaryembodiment, without individually encoding the basic quantizationparameter.

The above-mentioned configuration and operations further enableeffective parallel processing similar to the second exemplary embodimentof the present invention. Specifically, referring to FIG. 9B, theprocessor A performs the first subblock quantization parameter decodingfor the basic block instead of the basic block quantization parameterdecoding. This processing replaces the basic block quantizationparameter decoding and the first subblock quantization parameterdifference value decoding. This means that, at the first stage ofparallel processing, the processors B and C need to wait until theprocessor A completes the decoding of the first subblock quantizationparameter. Subsequently, the processors B and C can start thereproduction of all subblock quantization parameters without waitinguntil the processor A completes the processing of other subblocks.

Although, in the fourth exemplary embodiment, the Golomb code is used todecode the basic block quantization parameter, the subblock quantizationparameter difference value, and the quantization coefficient, theprocessing is not limited thereto. It is of course possible to use, forexample, Huffman coding and other arithmetic coding methods.

When there is provided a code for switching between the method forcoding the basic block quantization parameter in the third exemplaryembodiment and the method for considering the first subblockquantization parameter as a basic block quantization parameter in thefourth exemplary embodiment, the image decoding apparatus interprets thecode and executes step S102 in FIG. 8. Alternatively, the image decodingapparatus preferably selects whether steps S310, S311, and S303 in FIG.15 are to be executed.

Although the fourth exemplary embodiment has specifically been describedbased on frames using intra-prediction, it is apparent that the presentexemplary embodiment is also applicable to frames that can useinter-prediction involving motion compensation in prediction.

A fifth exemplary embodiment of the present invention will be describedbelow based on the determination of the basic block quantizationparameter by using the subblock quantization parameter in the last basicblock.

An image coding apparatus according to the fifth exemplary embodimenthas a similar configuration to the image coding apparatus according tothe third exemplary embodiment of the present invention (FIG. 10), witha difference in the configuration of the quantization parameter codingunit 1208.

FIG. 16 is a block diagram illustrating a detailed configuration of thequantization parameter coding unit 1208 according to the fifth exemplaryembodiment of the present invention.

Referring to FIG. 16, a selector 400 selects a source depending on thebasic block position for the input subblock quantization parameter. Asubblock quantization parameter storage unit 410 stores the subblockquantization parameters of the preceding basic block. A basic blockquantization parameter determination unit 403 determines a basic blockquantization parameter of the basic block subjected to coding based onthe subblock quantization parameters stored in the subblock quantizationparameter storage unit 410. A subblock quantization parameter differenceunit 406 calculates a difference value between the basic blockquantization parameter and each subblock quantization parameter. Asubblock quantization parameter coding unit 407 encodes the differencevalue between the first subblock quantization parameter and eachsubblock quantization parameter.

With the above-mentioned configuration, similar to the third exemplaryembodiment, the block division unit 1001 divides image data (input fromthe terminal 1000) into a plurality of subblocks, and the quantizationparameter determination unit 1002 determines each subblock quantizationparameter. The quantization parameter determination unit 1002 outputseach determined subblock quantization parameter to the quantizationparameter coding unit 1208.

Referring to FIG. 16, when the input subblock quantization parameter isthe first subblock quantization parameter in the first basic block ofthe image data, the selector 400 selects an input from the terminal 1.The basic block quantization parameter determination unit 403 inputs thesubblock quantization parameter via the subblock quantization parameterstorage unit 410, the subblock quantization parameter difference unit406, and the selector 400. The subblock quantization parameter storageunit 410 stores the subblock quantization parameter for processing ofthe following basic block. Similar to the basic block quantizationparameter storage unit 203 according to the third exemplary embodiment,the basic block quantization parameter determination unit 403 stores theinput subblock quantization parameter as a basic block quantizationparameter. Similar to the subblock quantization parameter differenceunit 206 according the third exemplary embodiment of the presentinvention, the subblock quantization parameter difference unit 406outputs the subblock quantization parameter as it is to the subblockquantization parameter coding unit 407. The subblock quantizationparameter coding unit 407 encodes the first subblock quantizationparameter through Golomb coding, and outputs the resultant code to theoutside via the terminal 8.

Subsequently, the subblock quantization parameter storage unit 410 andthe subblock quantization parameter difference unit 406 inputs othersubblock quantization parameters of the first basic block of the imagedata from the terminal 1. The subblock quantization parameter differenceunit 406 calculates a difference value between the basic blockquantization parameter output from the basic block quantizationparameter determination unit 403 and the input subblock quantizationparameter. The subblock quantization parameter coding unit 407 inputsthe difference value, encodes the difference value similar to the thirdexemplary embodiment, and outputs the resultant code to the outside viathe terminal 8.

Processing for subsequently input basic blocks of the image, not thefirst basic block, will be described below. Prior to the codingprocessing for a basic block, the selector 400 selects the subblockquantization parameter storage unit 410 as a source. The basic blockquantization parameter determination unit 403 calculates an average ofthe stored subblock quantization parameters, and considers the averageas a basic block quantization parameter. Then, the subblock quantizationparameter difference unit 406 inputs the subblock quantizationparameters of the relevant basic block from the terminal 1. The subblockquantization parameter difference unit 406 calculates a difference valuebetween the basic block quantization parameter output from the basicblock quantization parameter determination unit 403 and each inputsubblock quantization parameter. The subblock quantization parametercoding unit 407 inputs a difference value, encodes the difference valuesimilar to the third exemplary embodiment, and outputs the resultantcode to the terminal 8.

FIG. 17 is a flowchart illustrating image coding processing by the imagecoding apparatus according to the fifth exemplary embodiment of thepresent invention. Referring to FIG. 17, elements having the samefunction as those in the first exemplary embodiment (FIG. 4) areassigned the same reference numerals and duplicated descriptions will beomitted.

In steps S001 to S003, similar to the image coding apparatus accordingto the first exemplary embodiment, the image coding apparatus encodesthe header information, clips a basic block from image data, and dividesthe basic block into a plurality of subblocks. In step S401, the imagecoding apparatus determines whether the relevant basic block is thefirst basic block of the image. When the relevant basic block is thefirst basic block (YES in step S401), the processing proceeds to stepS402. Otherwise, when the relevant basic block is not the first basicblock (NO in step S401), the processing proceeds to step S409. In stepS402, the image coding apparatus determines whether the relevantsubblock is the first subblock in the first basic block. When therelevant subblock is the first subblock (YES in step S402), theprocessing proceeds to step S403. Otherwise, when the relevant subblockis not the first subblock (NO in step S402), the processing proceeds tostep S406.

In step S403, the image coding apparatus determines a first subblockquantization parameter of the first basic block, and stores the firstsubblock quantization parameter so as to be referred to duringprocessing of the following basic block. In step S404, the image codingapparatus stores the subblock quantization parameter determined in stepS403 as a basic block quantization parameter. In step S405, the imagecoding apparatus encodes the subblock quantization parameter determinedin step S403, and the processing proceeds to step S008. In step S406,the image coding apparatus determine a subblock quantization parameterof the relevant subblock, and stores the determined subblockquantization parameter so as to be referred to during processing of thefollowing basic block.

In step S407, the image coding apparatus subtracts the basic blockquantization parameter stored in step S404 from the subblockquantization parameter determined in step S406 to calculate a subblockquantization parameter difference value of the relevant subblock. Instep S408, the image coding apparatus encodes the subblock quantizationparameter difference value calculated in step S407 to generatequantization parameter difference value coded data, and the processingproceeds to step S008. In step S409, the image coding apparatusdetermines whether the relevant subblock is the first subblock in thesecond and subsequent basic block. When the relevant subblock is thefirst subblock (YES in step S409), the processing proceeds to step S410.Otherwise, when the relevant subblock is not the first subblock (NO instep S409), the processing proceeds to step S406. In step S410,referring to the subblock quantization parameters of the preceding basicblock stored in step S403 or S406, the image coding apparatus calculatesthe basic block quantization parameter of the relevant basic block. Inthe present exemplary embodiment, the image coding apparatus calculatesan average of the above-mentioned subblock quantization parameters, andconsiders the average as a basic block quantization parameter. In stepS411, the image coding apparatus determines a subblock quantizationparameter of the relevant subblock, and stores the subblock quantizationparameter so as to be referred to during processing of the followingbasic block.

In step S412, the image coding apparatus subtracts the basic blockquantization parameter calculated in step S410 from the subblockquantization parameter determined in step S411 to calculate a subblockquantization parameter difference value of the relevant subblock.

In step S413, the image coding apparatus encodes the subblockquantization parameter difference value calculated in step S412 togenerate quantization parameter difference value coded data, and theprocessing proceeds to step S008. In step S414, the image codingapparatus determines whether coding processing is completed for all thesubblocks in the relevant basic block. When coding processing iscompleted for all the subblocks (YES in step S414), the processingproceeds to step S011. Otherwise, when coding processing is notcompleted for all the subblocks (NO in step S414), the processingreturns to step S401 to process the following subblock. In steps S008,S009, and S011, the image coding apparatus performs similar processingto the first exemplary embodiment to encode the entire image.

With the above-mentioned configuration and operations, determining thebasic block quantization parameter by using the subblock quantizationparameters of the preceding basic block enables determining the basicblock quantization parameter of the relevant basic block immediatelyafter starting the processing of the relevant basic block, resulting ina minimized processing delay. Further, calculating the basic blockquantization parameter based on the subblock quantization parameters ofthe preceding basic block eliminates the need of transferring the basicblock quantization parameter, resulting in improved coding efficiency.

The above-mentioned configuration and operations further enableeffective parallel processing similar to the first exemplary embodimentof the present invention. Specifically, referring to FIG. 5B, beforecoding processing, the basic block quantization parameter is calculatedbased on the subblock quantization parameters of the preceding basicblock. This enables calculating the quantization parameter differencevalues of all subblocks without waiting for completion of processing ofeach individual subblock.

Although, in the fifth exemplary embodiment, the first subblockquantization parameter is encoded as it is only for the first basicblock of the image, the processing is not limited thereto. Specifically,it is also possible to provide a slice-like configuration composed of aplurality of basic blocks, and apply similar processing to the firstbasic block.

Although, in the fifth exemplary embodiment, the basic blockquantization parameter is determined referring to the subblockquantization parameters of the preceding basic block, the processing isnot limited thereto. The last subblock quantization parameters of thepreceding basic block may be considered as a basic block quantizationparameter of the relevant basic block. It is of course possible to referto the subblock quantization parameters or the basic block quantizationparameter of the surrounding basic blocks.

Although, in the fifth exemplary embodiment, an average of subblockquantization parameters of the preceding basic block is considered as abasic block quantization parameter, the processing is not limitedthereto. It is of course possible, for example, that the basic blockquantization parameter may be a median of subblock quantizationparameters, or a most frequent subblock quantization parameter value. Itis of course possible to prepare a plurality of calculation methods inthis way, select a most efficient basic block quantization parameter,and perform coding by using a code indicating the relevant calculationmethod.

Although the fifth exemplary embodiment has specifically been describedbased on frames using intra-prediction, it is apparent that the presentexemplary embodiment is also applicable to frames that can useinter-prediction involving motion compensation in prediction.

A sixth exemplary embodiment of the present invention will be describedbelow based on an image decoding method for decoding code data coded byusing the coding method according to the fifth exemplary embodiment ofthe present invention. An image coding apparatus according to the sixthexemplary embodiment has a similar configuration to the image codingapparatus according to the fourth exemplary embodiment of the presentinvention (FIG. 13), with a difference in the configuration of thequantization parameter decoding unit 1302.

FIG. 18 is a block diagram illustrating a configuration of thequantization parameter decoding unit 1302 according to the sixthexemplary embodiment of the present invention. Referring to FIG. 18,elements having the same function as those in the fourth exemplaryembodiment (FIG. 14) are assigned the same reference numerals andduplicated descriptions will be omitted.

A selector 500 selects a destination depending on the subblock positionfor the input subblock quantization parameter and on the basic blockposition for the relevant subblock. A subblock quantization parameterdecoding unit 501 decodes a code of a subblock quantization parameteritself to reproduce a subblock quantization parameter. A subblockquantization parameter difference value decoding unit 502 decodes a codeof a subblock quantization parameter difference value to reproduce asubblock quantization parameter difference value. A selector 503 selectsa source depending on the subblock position for the input subblockquantization parameter and on the basic block position for the relevantsubblock. A basic block quantization parameter determination unit 504determines a basic block quantization parameter. A subblock quantizationparameter adding unit 505 adds the determined basic block quantizationparameter and each subblock quantization parameter difference value toreproduce each subblock quantization parameter. A selector 506 selects asource depending on the subblock position for the input subblockquantization parameter and on the basic block position for the relevantsubblock. A subblock quantization parameter storage unit 507 stores thereproduced subblock quantization parameters.

Decoding processing by the image decoding apparatus will be describedbelow. Although, in the present exemplary embodiment, a moving image bitstream is input in frame units, a still image bit stream for one framemay be input.

Prior to the decoding processing of a bit stream for one frame, theselector 500 selects the subblock quantization parameter decoding unit501 as a destination, and the selector 503 selects the subblockquantization parameter decoding unit 501 as a source. The selector 505selects the subblock quantization parameter decoding unit 501 as asource.

The subblock quantization parameter decoding unit 501 inputs thesubblock quantization parameter coded data of the first basic block viathe selector 500. The subblock quantization parameter decoding unit 501decodes the coded data by using the Golomb code to reproduce a subblockquantization parameter. The basic block quantization parameterdetermination unit 504 inputs the subblock quantization parameter viathe selector 503. Since the subblock of the subblock quantizationparameter is the first subblock of the first basic block, the basicblock quantization parameter determination unit 504 stores the inputsubblock quantization parameter as it is as a basic block quantizationparameter. The subblock quantization parameter decoding unit 501 outputsthe reproduced subblock quantization parameter to the outside via theselector 505 and the terminal 106. The subblock quantization parameterstorage unit 507 stores the subblock quantization parameter.

Subsequently, the selector 500 selects the subblock quantizationparameter difference value decoding unit 502 as a destination, and theselector 503 selects the subblock quantization parameter storage unit507 as a source. The selector 505 selects the subblock quantizationparameter adding unit 305 as a source.

When the quantization parameter decoding unit 1302 inputs the subblockquantization parameter difference value coded data of the followingsubblock, the subblock quantization parameter difference value decodingunit 502 inputs the subblock quantization parameter difference valuecoded data via the selector 500. The subblock quantization parameterdifference value decoding unit 502 decodes the subblock quantizationparameter difference value coded data to reproduce a subblockquantization parameter difference value. The subblock quantizationparameter adding unit 305 adds the subblock quantization parameterdifference value to the basic block quantization parameter to reproducea subblock quantization parameter, and outputs the reproduced subblockquantization parameter to the outside via the terminal 106. The subblockquantization parameter storage unit 507 stores the subblock quantizationparameter.

Subsequently, the quantization parameter decoding unit 1302 inputs thesubblock quantization parameter difference value coded data of thefollowing basic block. In this case, the basic block quantizationparameter determination unit 504 reads the subblock quantizationparameters of the preceding basic block from the subblock quantizationparameter storage unit 507, calculates an average of the read subblockquantization parameters, and considers the average as a basic blockquantization parameter of the relevant basic block.

The subblock quantization parameter difference value decoding unit 502decodes the input subblock quantization parameter difference value codeddata to reproduce a subblock quantization parameter difference value.The subblock quantization parameter adding unit 305 reproduces asubblock quantization parameter, and outputs the reproduced subblockquantization parameter to the outside via the terminal 106. The subblockquantization parameter storage unit 507 stores the reproduced subblockquantization parameter.

Subsequently, the quantization parameter decoding unit 1302 inputsfollowing subblock quantization parameter difference value coded data,similarly reproduces a subblock quantization parameter difference value,and then reproduces a subblock quantization parameter, the quantizationparameter decoding unit 1302 outputs the reproduced subblockquantization parameter to the outside via the terminal 106. The subblockquantization parameter storage unit 507 stores the subblock quantizationparameter.

FIG. 19 is a flowchart illustrating image decoding processing by animage decoding apparatus according to the sixth exemplary embodiment ofthe present invention.

In step S101, similar to the second exemplary embodiment of the presentinvention, the image decoding apparatus decodes the header information.In step S501, the image decoding apparatus determines whether the basicblock of the subblock subjected to decoding is the first basic block ofthe image. When the relevant basic block is the first basic block (YESin step S501), the processing proceeds to step S502. Otherwise, when therelevant basic block is not the first basic block (NO in step S501), theprocessing proceeds to step S504.

In step S502, the image decoding apparatus determines whether thesubblock subjected to decoding is the first subblock in the basic block.When the relevant subblock is the first subblock block (YES in stepS502), the processing proceeds to step S503. Otherwise, when therelevant subblock is not the first subblock block (NO in step S502), theprocessing proceeds to step S506. In step S503, the image decodingapparatus decodes the code related to the input subblock quantizationparameter, i.e., the subblock quantization parameter coded data by usingthe Golomb code to reproduce a subblock quantization parameter. Theimage decoding apparatus stores the resultant code as a basic blockquantization parameter. At the same time, the image decoding apparatusseparately stores the resultant code so as to be referred to duringdetermination of the basic block quantization parameter of the followingbasic block. Then, the processing proceeds to step S104 for decodedimage generation of the first subblock.

In step S504, the image decoding apparatus determines whether thesubblock subjected to decoding is the first subblock in the basic block.When the subblock subjected to decoding is the first subblock (YES instep S504), the processing proceeds to step S505. Otherwise, when thesubblock subjected to decoding is not the first subblock (NO in stepS504), the processing proceeds to step S506.

In step S505, the image decoding apparatus calculates an average of thestored subblock quantization parameters of the preceding basic block,and considers the average as a basic block quantization parameter. Then,the processing proceeds to step S506.

In step S506, the image decoding apparatus decodes the code related tothe input subblock quantization parameter, i.e., the subblockquantization parameter difference value coded data by using the Golombcode to reproduce a subblock quantization parameter difference value.The image decoding apparatus adds the reproduced subblock quantizationparameter difference value to the basic block quantization parameterstored or calculated in step S503 or S505 to obtain a subblockquantization parameter. Then, the processing proceeds to step S104 fordecoded image generation of the subblock. Subsequently, similar to thefourth exemplary embodiment of the present invention, the image decodingapparatus generates a subblock decoded image and reproduces a frameimage.

The above-mentioned configuration and operations enable decoding a bitstream with which the basic block quantization parameter value generatedby the image coding apparatus according to the fifth exemplaryembodiment is not coded.

The above-mentioned configuration and operations further enableeffective parallel processing similar to the second exemplary embodimentof the present invention. Specifically, referring to FIG. 9B, instead ofthe basic block quantization parameter decoding, the processor Aperforms the basic block quantization parameter calculation by usingsubblock quantization parameters of the preceding basic block. Thisenables the processor A to start the quantization parameter reproductionfor all the subblocks without waiting for completion of processing onother subblocks.

Although, in the sixth exemplary embodiment, an average of subblockquantization parameters of the preceding basic block is considered as abasic block quantization parameter, the processing is not limitedthereto as long as the method for calculating the basic blockquantization parameter according to the fifth exemplary embodiment isused. It is of course possible, for example, that the basic blockquantization parameter may be a median of subblock quantizationparameters, or a most frequent subblock quantization parameter value.These pieces of information can be derived from the subblockquantization parameters stored in the subblock quantization parameterstorage unit 507.

Even when a plurality of calculation methods is prepared in this way onthe coding side, a most efficient basic block quantization parameter isselected, and coding is performed based on a code indicating therelevant calculation method, the subblock quantization parameter can besimilarly calculated through decoding.

Although the sixth exemplary embodiment has specifically been describedbased on frames using intra-prediction, it is apparent that the presentexemplary embodiment is also applicable to frames that can useinter-prediction involving motion compensation in prediction.

Although the above-mentioned exemplary embodiments have specificallybeen described on the premise that the processing units illustrated inFIGS. 1, 3, 6, 7, 10, 11, 13, 14, 16, and 18 are implemented byhardware, processing executed by these processing units may beimplemented by software (computer programs).

FIG. 20 is a block diagram illustrating an example hardwareconfiguration of a computer applicable to the image display unitaccording to the above-mentioned exemplary embodiments of the presentinvention.

A central processing unit (CPU) 1401 controls the entire computer byusing computer programs and data stored in a random access memory (RAM)1402 and a read-only memory (ROM) 1403, and executes each piece ofprocessing described above as the image processing apparatus accordingto the above-mentioned exemplary embodiments. Specifically, the CPU 1401functions as the processing units illustrated in FIGS. 1, 3, 6, 7, 10,11, 13, 14, 16, and 18.

The RAM 1402 includes an area for temporarily storing a computer programand data loaded from an external storage device 1406, and data acquiredfrom the external via an interface (I/F) 1407. The RAM 1402 furtherincludes work areas used by the CPU 1401 to execute various pieces ofprocessing. For example, the RAM 1402 can be used as a frame memory andother various types of areas as required.

The ROM 1403 stores setting data and a boot program of the computer. Anoperation unit 1404 is provided with a keyboard, a mouse, etc. A user ofthe computer operates the operation unit 1404 to give variousinstructions to the CPU 1401. An output unit 1405 displays a result ofprocessing executed by the CPU 1401. The output unit 1405 is composed ofa hold-type display unit such as a liquid crystal display (LCD) or animpulse-type display unit such as a field emission type display unit.

The external storage device 1406 is a mass storage device represented bya hard disk drive unit. The external storage device 1406 stores anoperating system (OS) and computer programs executed by the CPU 1401 toimplement the functions of the processing units illustrated in FIGS. 1,3, 6, 7, 10, 11, 13, 14, 16, and 18. The external storage device 1406may further store image data to be processed.

The CPU 1401 suitably loads a computer program and data stored in theexternal storage device 1406 into the RAM 1402, and executes thecomputer program. Networks such as a local area network (LAN) and theInternet, a projection device, a display device, and other devices canbe connected to the I/F 1407. The computer can acquire and transmitvarious pieces of information via the I/F 1407. A bus 1408 interconnectsthe above-mentioned various devices.

Operations with the above-mentioned configuration are achieved when theCPU 1401 controls the processing of the above-mentioned flowcharts.

Further, when the CPU 1401 has a multi-core configuration, efficientparallel processing can be achieved by assigning a thread of each pieceof processing to each core.

The present invention is also achieved when a storage medium recordingcomputer program codes for implementing the above-mentioned functions issupplied to a system, and the system loads and executes the computerprogram codes. In this case, the computer program codes loaded from thestorage medium implement the functions of the exemplary embodiments, andthe storage medium storing the computer program codes constitutes thepresent invention. Further, the present invention further includes acase where the operating system (OS) operating on the computer executesa part or whole of actual processing based on instructions of thecomputer program codes, and the above-mentioned functions areimplemented by the processing of the computer program codes.

Further, the present invention may be achieved by the following form.Specifically, the present invention further includes a case wherecomputer program codes loaded from the storage medium are written to amemory provided in a function expansion card inserted into the computeror a function expansion unit connected to the computer. The presentinvention further includes a case where a CPU provided in the functionexpansion card or function expansion unit executes a part or whole ofactual processing based on instructions of the computer program codes toimplement the above-mentioned functions.

When applying the present invention to the above-mentioned storagemedium, the storage medium stores the computer program codescorresponding to the above-described flowcharts.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all modifications, equivalent structures, and functions.

1. An image coding apparatus comprising: a division unit configured todivide an input image into a plurality of blocks, at least one of theblocks being divided into subblocks so as to form a quadtree; a decisionunit configured to decide respective quantization parameters of thesubblocks; an acquisition unit configured to acquire a first differencevalue between a first quantization parameter of a first subblock of thesubblocks and a second quantization parameter of a second subblock ofthe subblocks, the first subblock to be coded before the secondsubblock, and to acquire a second difference value between a thirdquantization parameter of a third subblock of the subblocks and a valuecorresponding to an average of quantization parameters of subblockswhich are to be coded before the third subblock; and a coding unitconfigured to code the first difference value and the second differencevalue.
 2. The apparatus according to claim 1, wherein the first subblockis arranged at the upper left of the block.
 3. The apparatus accordingto claim 1, wherein the value corresponding to the average is anapproximate value of the average or a value of the average.
 4. An imagedecoding apparatus for decoding quantization parameters for subblocks ina block representing a part of an image, wherein the block is dividedinto subblocks so as to form a quadtree, the image decoding apparatuscomprising: a decoding unit configured to decode a first quantizationparameter for a first subblock, coded data related to a first differencevalue between the first quantization parameter for the first subblockand a second quantization parameter for a second subblock, and codeddata related to a second difference value between a third quantizationparameter for a third subblock and a value corresponding to an averageof quantization parameters for subblocks in the block, wherein the firstsubblock, the second subblock, and the third subblock are generated bydividing the block so as to form a quadtree; an acquisition unitconfigured to acquire the second quantization parameter based on thefirst quantization parameter and the first difference value decoded bythe decoding unit, and acquire the third quantization parameter based onthe second difference value decoded by the decoding unit and the valuecorresponding to the average of quantization parameters for subblocksdecoded before the third subblock.
 5. The apparatus according to claim4, wherein the first subblock is arranged at the upper left of theblock.
 6. The apparatus according to claim 4, wherein the valuecorresponding to the average is an approximate value of the average or avalue of the average.
 7. A method for an image coding apparatus, themethod comprising: dividing an input image into a plurality of blocks,at least one of the blocks being divided into subblocks so as to form aquadtree; deciding respective quantization parameters of the subblocks;acquiring a first difference value between a first quantizationparameter of a first subblock of the subblocks and a second quantizationparameter of a second subblock of the subblocks, the first subblock tobe coded before the second subblock, and acquiring a second differencevalue between a third quantization parameter of a third subblock of thesubblocks and a value corresponding to an average of quantizationparameters of subblocks which are to be coded before the third subblock;and coding the first difference value and the second difference value.8. The method according to claim 7, wherein the first subblock isarranged at the upper left of the block.
 9. The method according toclaim 7, wherein the value corresponding to the average is anapproximate value of the average or a value of the average.
 10. A methodfor an image decoding apparatus for decoding quantization parameters forsubblocks in a block representing a part of an image, wherein the blockis divided into subblocks so as to form a quadtree, the methodcomprising: decoding a first quantization parameter for a firstsubblock, coded data related to a first difference value between thefirst quantization parameter for the first subblock and a secondquantization parameter for a second subblock, and coded data related toa second difference value between a third quantization parameter for athird subblock and a value corresponding to an average of quantizationparameters for subblocks in the block, wherein the first subblock, thesecond subblock, and the third subblock are generated by dividing theblock so as to form a quadtree; acquiring the second quantizationparameter based on the first quantization parameter and the firstdifference value decoded by the decoding, and acquiring the thirdquantization parameter based on the second difference value decoded bythe decoding and the value corresponding to the average of quantizationparameters for subblocks decoded before the third subblock.
 11. Themethod according to claim 10, wherein the first subblock is arranged atthe upper left of the block.
 12. The method according to claim 10,wherein the value corresponding to the average is an approximate valueof the average or a value of the average.
 13. A non-transitory computerreadable storage medium for storing instructions that, when executed,cause an image coding apparatus to perform a process, the processcomprising: dividing an input image into a plurality of blocks, at leastone of the blocks being divided into subblocks so as to form a quadtree;deciding respective quantization parameters of the subblocks; acquiringa first difference value between a first quantization parameter of afirst subblock of the subblocks and a second quantization parameter of asecond subblock of the subblocks, the first subblock to be coded beforethe second subblock, and acquiring a second difference value between athird quantization parameter of a third subblock of the subblocks and avalue corresponding to an average of quantization parameters ofsubblocks which are to be coded before the third subblock; and codingthe first difference value and the second difference value.
 14. Thenon-transitory computer readable storage medium according to claim 13,wherein the first subblock is arranged at the upper left of the block.15. The non-transitory computer readable storage medium according toclaim 13, wherein the value corresponding to the average is anapproximate value of the average or a value of the average.
 16. Anon-transitory computer readable storage medium for storing instructionsthat, when executed, cause an image decoding apparatus to perform aprocess, wherein the image decoding apparatus decodes quantizationparameters for subblocks in a block representing a part of an image, theblock divided into subblocks so as to form a quadtree, the processcomprising: decoding a first quantization parameter for a firstsubblock, coded data related to a first difference value between thefirst quantization parameter for the first subblock and a secondquantization parameter for a second subblock, and coded data related toa second difference value between a third quantization parameter for athird subblock and a value corresponding to an average of quantizationparameters for subblocks in the block, wherein the first subblock, thesecond subblock, and the third subblock are generated by dividing theblock so as to form a quadtree; acquiring the second quantizationparameter based on the first quantization parameter and the firstdifference value decoded by the decoding, and acquiring the thirdquantization parameter based on the second difference value decoded bythe decoding and the value corresponding to the average of quantizationparameters for subblocks decoded before the third subblock.
 17. Thenon-transitory computer readable storage medium according to claim 16,wherein the first subblock is arranged at the upper left of the block.18. The non-transitory computer readable storage medium according toclaim 16, wherein the value corresponding to the average is anapproximate value of the average or a value of the average.